To clarify the mechanism of spontaneous oxidative exothermic reaction of coal, we have been analyzing the molecular structure of coal before and after oxidation. As a result, radical formation during the oxidation reaction was suggested. Therefore, in this study, ESR spectral measurements were performed while the coal was heated under an oxygen atmosphere. The higher the spontaneous exothermicity of coal, the more radicals increased immediately after the switch from nitrogen to oxygen in the atmosphere. This is expected to lead to a more detailed elucidation of the mechanism of natural heat generation in coal in the future.
